The present invention relates to power transmission devices which can absorb axial impact energy for use, e.g. in propeller shafts and steering columns for motor vehicles.
One of the power transmission devices of this type is disclosed, e.g. in U.S. Pat. No. 4,183,258 wherein a shaft and a tube engaged therewith are interconnected by a spline joint to relatively be movable in the axial direction and not to relatively be rotatable in the direction of rotation, and they are also interconnected by a breakable pin arranged through through holes of the shaft and the tube.
The power transmission device ensures torque transmission between the shaft and the tube. When axially undergoing a force or impact greater than a predetermined value, the device absorbs impact energy through relative axial movement of the shaft and the tube produced by breaking of the breakable pin.
With the known power transmission device, the breakable pin is arranged through the through hole of the shaft and that of the tube which has outer peripheral openings communicating with the air. As a consequence, when the shaft and the tube are rotated for power transmission, the breakable pin can be disengaged with the through holes. Moreover, when muddy water, etc. enter the through holes from the outer peripheral openings, the breakable pin may be corroded by formation of rust to vary its breaking load, resulting in impossible achievement of a desired impact absorbing effect.
It is, therefore, an object of the present invention to provide power transmission devices with impact absorbing potential, which allow sure and constant engagement of the component parts, and stable impact absorbing effect.